Low vision is a general term used to describe lowered visual acuity, and a specific legal term in Canada and the United States used to designate someone with vision of 20/70 or less in the better eye with correction. It can be a result of either congenital or acquired factors. An example of the former is Leber's congenital amaurosis and of the latter age related macular degeneration.
Some people with low vision can use their residual vision—their remaining sight—to complete daily tasks without relying on alternative methods. The role of a low vision specialist is to maximize the functional level of a patient's vision by optical or non-optical means. Primarily, this is by use of magnification in the form of telescopic systems for distance vision and optical or electronic magnification for near tasks.
Visually impaired patients may benefit from high-tech aids such as OCR scanners that can, in conjunction with text-to-speech software, read the contents of books and documents aloud via computer. Vendors also build closed-circuit televisions that electronically magnify paper, and even change its colour contract, for visually impaired users.
The vast majority of patients with low vision can be helped to function at a higher level with the use of low vision devices. Low vision specialists recommend appropriate low vision devices and counsel patients on how better to deal with their reduced vision in general. See, for example, Computer Resources for People With Disabilities: A Guide to Assistive Technologies Tools and Resources for People of All Ages, Alliance for Technology Access, Hunter House, Inc. Publishers, 2004; and In Sight: Guide to Design with Low Vision in Mind, Lucienne Roberts, Rotovision 2004 which are incorporated herein by reference.
The use of a CCTV or video magnifier is a simple way providing access to classrooms and public events to people with low vision. In the classroom setting, for example, printed material and objects displayed at the front of the room can be captured by a camera and the magnified image is displayed on a television screen or computer monitor. There are a large number of different types of models to choose from and they vary widely in the features offered.
For example, U.S. Pat. No. 6,731,326 to Bettinardi (which is incorporated herein by reference) describes a method of displaying information captured from a camera on a monitor. The camera captures an image and then allows the user to select a smaller portion for full, magnified, display. The '326 patent also provides a method of allowing the user to pan the image and zoom in on a desired area. The user, however, must recapture information as he moves from portion to portion of the image. This takes additional time as well as requiring significant resources from the processor controlling the display.
Of the commercially available distance cameras, a problem arises where a user wishes to toggle through various areas in the camera's line of sight. Continuing with the classroom example; a user may wish to pan and zoom such as where a chalkboard contains a large amount of written information. Previous devices required a user to recapture information when a user desired to scroll back, perhaps to review some previous information. The need to recapture the image of the chalkboard creates a cumbersome interface, as well as wasting computer resources.